The invention relates to processes for fabricating dynamic random access memories, and more particularly to the deposition of tungsten nitride.
Tungsten nitride has been shown to be an extremely promising material for planar capacitor and gate electrode applications. Tungsten nitride is stable at high temperatures and prevents dielectric degradation in capacitor applications and acts as a barrier between polycrystalline silicon and tungsten when used as a low resistivity strapping layer in a gate electrode. In one fabrication method Alex Lahav, Karen A. Grim, and Ilan A. Blech, as described in their article, xe2x80x9cMeasurement of Thermal Expansion Coefficients of W, WSi, WN, and WSiN Thin Film Metallizations,xe2x80x9d Journal of Applied Physics 67(2), Jan. 15, 1990, page 734, prepare tungsten nitride using reactive sputtering and obtain good film properties.
Although sputtering can provide high quality films, surface step coverage is inadequate for many applications. It would be preferred to have an improved step coverage process such as chemical vapor deposition (CVD).
Nakajima et al. in an article entitled xe2x80x9cPreparation of Tungsten Nitride Film by CVD Method Using WF6xe2x80x9d appearing in the December 1987 edition of the Journal of Electrochemical Society: SOLID-STATE SCIENCE AND TECHNOLOGY, has demonstrated chemical vapor deposition of tungsten nitride from NH3 and WF6 source gases in a conventional hot wall CVD system. Although hot wall CVD systems offer an advantage with respect to wafer throughput, process control and cleanliness are typically not adequate for state-of-the-art applications. Rather, single wafer cold wall deposition systems are preferred.
For a CVD process WF6 and NH3 offer the advantages of being readily available and providing high deposition rates. However, WF6 and NH3 form an adduct at low temperatures ( less than 50xc2x0 C.), and even with a cold wall system there is a minimum acceptable wall temperature to prevent adduct formation. Furthermore, byproducts of the deposition reactions can cause encroachment into silicon or polycrystalline silicon substrates and therefore the process must be modified to reduce encroachment without compromising adhesion or resistivity.
Thus, there exists a need for a CVD tungsten nitride process having good adhesion and high deposition rates while providing conformal, low resistivity films with minimal silicon encroachment.
The invention is a method for depositing tungsten nitride using chemical vapor deposition. The method uses a source gas mixture having a silicon based gas for depositing the tungsten nitride to overlie a deposition substrate.
The method is useful in the fabrication of a capacitor electrode, a contact plug, and a gate electrode due to the good adhesion, minimal silicon encroachment and low resistivity of the tungsten nitride deposited according to the method of the invention.
The invention is a non-planar storage capacitor having a tungsten nitride capacitor electrode.